As armature coils for small-sized motors, there have heretofore been known armature coils manufactured by winding a printed coil into a cylindrical shape, as disclosed in Japanese Patent Laid-Open No. 55-147936 (1980), for example.
To date, armature coils fabricated using printed coils have been constructed as follows. An even number (this number is determined dependent on the number of phases, laminated layers and poles of the armature coil) of unit coils are printed on a belt-like, pliable and thin insulating material at respective predetermined positions, thereby forming a printed coil. The printed coil is wound into a cylindrical shape such that the r-th unit coil (1.ltoreq.r.ltoreq.P, where P is the number of poles of the armature coil) counting from an end of the printed coil is overlapped with the (P+r)-th and (2P+r)-th unit coils in terms of mechanical arrangement and electrical phase. Then, laminated layers of the wound printed coil are fixed to each other using an adhesive to provide an armature coil in which the respective unit coils are arranged at their predetermined positions.
Since the unit coils formed on the insulating material have all a constant width of conductors and a constant gap between the adjacent conductors, discrepancy between the inner peripheral side and the outer peripheral side in the cylindrically wound printed coil has been adjusted by varying a width of the area surrounded by the innermost periphery of spiral conductor pattern of each unit coil.
Use of such an armature coil comprising a printed coil wound into a cylindrical shape can make the gap between a rotor magnet and a stator core narrower than that in a wound-type motor having a hollow coil adhered. This is advantageous in reducing torque ripple with the more uniform magnetic flux density and hence providing a motor which exhibits a high torque characteristic without cogging (torque fluctuations).
In the printed coil, however, it is required for conductor foils to be etched deeply and narrowly in order to reduce the resistance value. Thus, operation has to be carried out under very strict etching conditions. Furthermore, conventional armature coils have not taken into account special care about the conductor pitch of a multiplicity of unit coils formed on an insulating material. With all conductors formed at equal intervals as mentioned above, etching had to be made very narrowly throughout the elongate printed coil. This has disadvantages in that operability is poor, throughput (yield, the same shall apply hereinafter) of the etching process is lowered, and hence the cost is increased.
In addition, for obtaining high rotational precision by assembling the armature coil into a motor, a plurality of unit coils are required to be overlapped with high accuracy. But, when a cylindrical armature coil is formed using the printed coil of conventional structure, a problem arises in that aligning operation is difficult and hence needs a lot of time.
Therefore, the motor using the armature coil of conventional structure is superior in performance, but poor in economy.
A method of laminating and fixing a printed coil in the conventional manufacture process of an armature coil will be described below.
The method of laminating and fixing a printed coil includes the steps of placing a thin, pliable insulator such as a polyester film on the surface of the printed coil to avoid contact between conductor patterns formed thereon, and winding the printed coil and the thin insulator together plural times (at this time, the thin insulator is so wound as to enter between every two laminated layers of the printed coil). Then, after temporary fixing as described later, an adhesive is applied between the printed coil and the thin insulator and between the adjacent thin insulators.
In the above process of laminating and fixing the printed coil, the wound coil obtained by winding the printed coil with the insulator interposed between the laminated layers is held in its cylindrical shape by temporarily fixing a trailing end of the insulator, which is made larger than the printed coil beforehand, to the adjoining inner peripheral layer using an adhesive or sticky tape. Thereafter, the adhesive is applied to fix between the printed coil and the thin insulator.
Therefore, such drawbacks have accompanied this method in that, in the temporarily fixed portion using a new adhesive or a sticky tape, the applied adhesive may have an uneven thickness, or the thickness is partially increased corresponding to that of the sticky tape, so that the finished armature coil may have its shape not uniform all around the circumference, and operability of the laminating and fixing process may become poor.